Scraper chain conveyors having large overall lengths are used in underground winning installations, such as in underground mining operations for example, these scraper chain conveyors being composed of individual pan sections which are connected to one another in a manner resistant to tension on the end side. The adjacent pan sections attached to one another are connected in particular via toggle pockets and toggles as pan-section connecting means which allow certain angular mobility of the adjacent pan sections in the horizontal and vertical so that the scraper chain conveyor can compensate for ground unevenness in the floor and can be moved along with the advance of the working face. If the pan sections are used for longwall face conveyors, they are provided with attachments on the goaf side and/or on the working-face side for guiding, for example, a winning plough or a shearer loader and have connecting brackets for an advancing beam buttressed at the face support. Improvements in the production output of the winning machines and increasing the face lengths up to 450 m in the meantime likewise increase the conveying output that the conveyors have to cope with, and modern face and gate conveyors must be able to cope with conveying capacities of at least 2000 t/h (metric tons/hour) and even 5000 t/h in the case of high-output conveyors. With increasing conveying capacity, the wear of individual pan sections inevitably increases and there is a need on the market for conveyor pans having a high conveying capacity and a long service life at the lowest possible production costs and low overall weight of the individual pan sections.
Modern underground face and gate conveyors can be divided into three groups with reference to the construction of the pan sections. The first group contains conveyors having completely cast pan sections. The advantage of such cast structures lies in their high reproducibility, in the high loading capacity on account of the homogeneous construction and in the low susceptibility to assembly errors. Disadvantages are the high material costs, the fact that individual zones cannot be easily designed for higher loads or longer service life and the fact that there is no possibility of exchanging wearing parts.
The second group forms “hybrid pans” which consist of cast parts on the one hand and of rolled parts on the other hand. EP 525 926 A1, for example, shows such a hybrid pan. Hybrid pans only need a small number of welds since, for example, the entire structure of the side cheek including side profile for guiding the scrapers in the runs of the conveyor and toggle pockets as part of the pan-section connecting means can be designed in one piece, whereas the conveyor bottom, as one of the highly loaded parts, is welded to the cast side cheeks.
Furthermore, it is known in the case of hybrid pans to subsequently weld on the pan-section connecting means and other attachments for shifting the conveyor or for guiding a winning machine (DE 39 05 324 A1).
The third group of pan sections consists entirely or more or less entirely of a welded structure and the invention proceeds from the structure which is known from EP 1 362 805 B1 and in which at least the side cheeks consist of rolled profiles having a profile shape which is asymmetrical over the height and which has an offset with step between a bottom leg and a top leg, to which offset an intermediate bottom connecting the rolled profiles virtually rigidly is welded. The offset results in an especially advantageous profile shape which makes it easier to weld on functional parts and attachments and reduces the requisite assembly steps for producing a pan section as a welded structure. The frame structure is stiffened centrally. An overlap of the pan section with the mounting pockets for toggles at one pan section and a set-back arrangement of mounting pockets at the other pan section are said to protect the rolled profiles and the conveyor bottom or the intermediate bottom from fatigue fractures.